A closer look at Iraq's use of chemical weapons, and connections with al Qaeda, appears to have explained the interest the September 11 attackers had in crop dusters. During the 1980s war with Iran, Iraq used crop dusters to drop chemical weapons (mustard and nerve gas) on Iranian troops. Thus Iraq has much practical experience using crop dusters with checmical weapons. There is also a fear that the terrorists efforts to obtain drivers permits for hazardous materials was directed more at pure terrorism than just killing a lot of people. A lot of deadly chemicals are available in liquid form. For example, lots of herbicide is hijacked (the stuff is worth up to $40 a gallon) and available via criminal gangs. A truckload of this highly toxic herbicides, with some holes drilled into the containers and then driven over highways near a large metropolitan area, could generate considerable panic and the need for an expensive clean up. A similar effect could be generated with a low level "dirty" nuclear bomb. Tons of low level nuclear material is moved around every day, or available in hospitals or industrial facilities (for irradiation and other manufacturing processes.) Add some of this nuclear material to explosives, set off in a city and watch the panic. The problem here is not high tech or availability, but simply determination on the part of the terrorists.